The present invention relates to phase change ink carrier compositions and to phase change inks produced therefrom which are useful in ink jet printing devices.
In general, phase change inks are in solid phase at ambient temperature, but exist in liquid phase at the elevated operating temperature of an ink jet printing device. Liquid phase ink jet drops at the operating temperature are ejected from the printing device and, when the ink drops contact the surface of a wide variety of printing media, they quickly solidify to form a predetermined pattern of solidified ink drops.
Phase change ink is desirable since it remains in a solid phase at room temperature, during shipping, long-term storage, etc. Also, the problems associated with nozzle clogging due to ink evaporation are largely eliminated, thereby improving the reliability of ink jet printing. Furthermore, since the ink droplets solidify immediately upon contact with the substrate, migration of ink along the printing medium is prevented and dot quality is improved.
The initial prior art on phase change inks for ink jet printing involved monochrome inks jetted by electrostatic printing devices. Thus, for example in U.S. 3,653,932, a low melting ink (30.degree. C. to 50.degree. C.) is provided employing an ink base comprising di-esters of sebacic acid In a similar process, U.S. Pat. No. 3,715,219 describes another low melting point ink (30.degree. C. to 60.degree. C.) comprising a paraffin alcohol-based ink However, when low melting point phase change inks are employed in printing onto a substrate, they exhibit offset problems, namely, when the printed substrates formed from these inks are stacked and stored for subsequent use, they can become adhered to one another, particularly if high ambient temperatures are experienced.
U.S. Pat. Nos. 4,390,369 and 4,484,948 describe methods for producing monochrome phase change inks which employ a natural wax ink base, such as Japan wax, candelilla wax, carnauba wax, etc., which is printed from a drop-on-demand ink jet device at a temperature ranging between 65.degree. C. and 75.degree. C. In U.S. Pat. No. 4,659,383, a monochrome ink composition is provided having an ink base comprising a C20-24 acid or alcohol, a ketone, and an acrylic resin plasticizer. These monochrome ink compositions are not durable and when printed can be smudged with routine handling and folding.
In Japanese patent application No. 128,053/78, amides which are solid at room temperature, such as acetamide, are employed as printing inks. U.S. Pat. No. 4,684,956 is directed to monochrome phase change inks utilizing synthetic microcrystalline wax (hydrocarbon wax) and microcrystalline polyethylene wax. This molten composition can be applied to a variety of porous and non-porous substrates using drop-on-demand ink jet application techniques.
Finally, EP Nos. 0187352 and 0206286 reference phase change ink jet printing in color. The ink bases for these systems comprise fatty acids, a thermoplastic polyethylene and a phase change material in the first application; and the alcohol portion of a thermal setting resin pair, a mixture of organic solvents (o-and p-toluene sulfonamide) and a dye in the second application.
Jet printing colored inks on to a light transmissive medium for displaying color images by overhead projection has historically been a problem. For example, in the case of aqueous inks, special coatings must be provided on the light transmissive medium in order to absorb the aqueous phase so that images of high quality are formed. See, for example, U.S. Pat. Nos. 4,503,111, 4,547,405 and 4,555,437. Even though special coatings are not required on receptor films used for phase change ink jet printing, when prior art color phase change inks are applied in a thin film of substantially uniform thickness to a light transmissive receiver sheet, they are not rectilinearly light transmissive. Therefore, they cannot be effectively employed for displaying color images by overhead projection techniques.
Therefore, a need exists for a phase change ink composition which is rectilinearly light transmissive as a thin film of substantially uniform thickness so that an image comprising intense colors of a predetermined pattern of the phase change ink can be visibly projected on an overhead projector, for example, the 3M Company's 413 Overhead Projector. The ink should also be durable and exhibit a single melting point transition at a relatively high temperature.